Substances which swell as a result of heat exposure thus increasing in volume and decreasing in density. Intumescents are typically endothermic to varying degrees, as they can contain chemically bound water. Intumescents are used in firestopping, fireproofing and gasketing applications. Some intumescents are susceptible to environmental influences such as humidity, which can reduce or negate their ability to function. DIBt approvals quantify the ability of intumescents to stand the test of time against various environmental exposures. DIBt approved firestops and fireproofing materials are available in Canada and the US. DIBt approvals have a finite validity and one must check the expiry date, which is printed on the front of the approval document.